This invention relates generally to implantable cardiac defibrillator devices for defibrillating the heart of a patient and more particularly, it relates to an implantable cardiac defibrillator employing improved sensing circuitry for processing ECG heart signals from the atrium and/or ventricle.
In recent years there has been substantial progress made in the research and development of defibrillating devices for providing an effective medical response to various disorders, such as ventricular fibrillation. Research effort has also been made toward developing improved sensing techniques for reliably monitoring heart activity so as to determine whether a defibrillating high energy shock is required.
However the implantable cardiac defibrillators of the prior art used comparatively simple sensing circuits. These prior art sensing circuits would typically include switched capacitor circuits. When it was desired to make a gain change, e.g., by switching in an additional capacitor, the output of the prior art switched capacitor circuits would experience a transient change referred to as a "glitch." For purposes of completeness, reference is made to an article entitled "High Resolution Switched Capacitor D/A Converter" by Roubik Gregorian in Microelectronics Journal, Vol. 12, No. 2, 1981, pp. 10-13. It would therefore be desirable to provide an implantable cardiac defibrillator employing improved sensing circuitry for processing ECG heart signals from the atrium and/or ventricle wherein the gain thereof may be changed without producing a transient or glitch on its output.
The present invention provides an implantable cardiac defibrillator employing a switched capacitor gain/filter stage whose gain can be changed without causing a transient on its output.